The present invention relates to an in-furnace slag level measuring method for predicting the occurrence of slopping in a refining period in a convertor, and an apparatus therefor.
Slag floating on a surface of molten metal in a convertor in a refining period foams according to factors for refining in the convertor, that is, according to factors such as the composition and viscosity of the slag, the oxygen content of the slag, etc. When the foaming of the slag progresses excessively, so-called slopping occurs to have a bad influence on the composition of the molten metal, the total yield of the refined product, etc. When such slopping progresses further, problems arise as to the reduction of workability, the reduction of the calorie of exhaust gas, the worsening of working environment such as production to red smoke, the damage of the apparatus, etc.
On the other hand, use of a slag foaming suppressing agent or suppressing of the amount of oxygen supplied for a lance to thereby reduce the amount of generated exhaust gas is considered from the point of view of prevention of the slopping of slag. However, use of an excessive amount of the slag foaming agent brings the following two disadvantages; increase in cost; and worsening of thermal efficiency caused by lowering of in-furnace temperature. Further, suppressing of the amount of supplied oxygen brings elongation of operation caused by reduction of reaction efficiency, that is, it brings worsening of the productivity.
Accordingly, not only prediction of slopping but grasping of the slag level in the convertor quantitatively and accurately for the proper operation of the convertor are necessary for the prevention of the occurrence of slopping.
Therefore, a technique for measuring the slag level in the convertor quantitatively has been considered. As the conventional technique, a radar type level meter using microwave capable of propagating straight even under the measuring environment that dust or flame is present in the convertor has been considered chiefly.
An example of the conventional slag level meter using a microwave radar has been disclosed in Japanese Patent Unexamined Publication No. Sho-63-21584. In the disclosed slag level meter, a microwave FMCW type radar antenna for a carrier frequency of about 10 GHz is fixed to an upper portion of a body of the convertor to transmit a microwave toward the surface of slag through the antenna. The propagation time required for the reciprocating motion of the microwave signal between the antenna and the slag surface, that is, the time from the point of time when the microwave signal is transmitted through the antenna to the point of time when the microwave signal is received through the antenna after reflected on the slag surface, is measured and converted into a distance. However, the conventional slag level meter has a disadvantage in that a shortage of sensitivity may arise in the FMCW type radar in the case where the surface of foamed slag is low in reflectivity with respect to such a microwave.
To solve the problem in the FMCW type radar, an improved slag level meter has been proposed in Japanese Patent Unexamined Publication No. Hei-2-98685 filed by the Assignee of the present invention. In the improved slag level meter, a pseudo random signal processing type microwave radar using a microwave with a carrier frequency of about 10 GHz is employed. In the slag level meter, a water-cooled antenna attached to an end of a water-cooled waveguide is inserted down into the convertor and then fixed. The propagation time required for the reciprocating motion of a microwave between the water-cooled antenna and the slag surface, that is, the time from the point of time when the microwave is transmitted through the water-cooled antenna to the point of time when the microwave signal is received through the water-cooled antenna after reflected on the slag surface, is measured and converted into a distance.
In those conventional techniques, it is necessary to secure an antenna fixture place or an antenna insertion hole in a hood being in the upper portion of the convertor, because the antenna must be provided in any case. However, space assignment for attaching the antenna to the hood is so complex that an increase in the equipment cost is brought, because attendant equipment of the convertor, such as a mainlance, a sublance, a sub-material supply hopper, a dust, etc. is provided with high density. In particular, in the case where a general convertor is rebuilt to attach the antenna thereto or in the case where a boiler piping is provided to the hood to recycle exhaust heat for the purpose of energy saving required in the recent years, the rebuilding of the hood is high in cost.